Find a caterer that has a wood fired pizza oven on a trailer. The pizza is unbelievable and everyone loves pizza.
Different games to build team cooperation, plus I would suggest a DJ that has the understanding of what games the company can play to generate friendly competition. If family members are invited a few games that can be played as a family unit or team.
My company used to have an inflatable obsticle course, volley ball, softball, a dunk tank to dunk the higher ups and we donated the money to charity, also an ice cream truck came and it was free, and a Dj with karoke. All the excutives manned the huge grill they rented....
It's for employees and their family. We don't want a "grand celebration", just a great time on a moderate budget.
Is it a family picnic or an employee's only picnic?
Is this a year in which you want to be having a grand celebration or is it a year to have a great time but on a lower budget?
First I would make sure you have enough volunteers so that everyone will have fun..If the picnic serves alcohol, have Kareoke. Have a clown pasing out balloons and face painting, have someone organize softball, vollyball, or kickball
Have you considered renting bikes or kayaks if you are near water? You could hire a band for a concert? Or do karaoke. Try to get everyone involved!